Method and device for producing a three-dimensional object

ABSTRACT

A method for producing a three-dimensional object (2) by applying layers of a pulverulent construction material (11) and by selectively solidifying said material by the action of energy comprises the steps: a layer of the pulverulent construction material (11) is applied to a support (6) or to a layer of the construction material that has been previously applied and at least selectively solidified; an energy beam (14) from an energy source (13) sweeps over points on the applied layer corresponding to a cross-section of the object (2) to be produced in order to selectively solidify the pulverulent construction material (11); and a gas flow (18) is guided in a main flow direction (RG) over the applied layer during the sweep of the energy beam (14). The main flow direction (RG) of the gas flow (G) and the sweep direction (RL) of the energy beam (14) are adapted to one another at least in one region of the cross-section to be solidified.

The present invention relates to a method and to a device for producinga three-dimensional object by solidifying build material layer by layerat the locations in the respective layer that correspond to the crosssection of the object to be produced through the introduction of energy.

Such methods are used for example for rapid prototyping, rapid toolingand rapid manufacturing. One example of such a method, which is known bythe name “selective laser sintering or laser melting,” and an associateddevice for carrying out the method are described in the document DE 19514 740 C1. According to this document, first a thin layer of thepulverulent build material is applied by way of a recoater, and thisbuild material is subsequently solidified at the locations thatcorrespond to the respective cross section of the object through theaction of a laser beam. These two steps are repeated in alternationuntil the three-dimensional object to be produced is finished.

For the mechanical properties of the object to be produced it may beadvantageous if the laser beam does not always scan the locations to besolidified in the same direction. Accordingly, DE 10 2007 014 683 A1describes a method for producing a three-dimensional object, in whichthe direction of substantially parallel solidification lines, alongwhich the laser scans the sections of the powder layer that correspondto a cross section of the object to be produced, is rotated from layerto layer about a specified angle. Additionally, this document describesa method in which the region to be scanned of the layer is divided intoelongate stripes and the individual stripes are exposed by way ofsequential scanning with the laser beam in a direction that istransverse to the longitudinal direction of the stripes.

During irradiation with the laser beam, depending on the type of thematerial used, in particular when sintering or melting metals, splashes,fumes and vapors are produced which expand into the build space. Inorder to avoid that these contaminations deposit on an input window forthe laser beam, DE 198 53 947 A1 proposes a process space in which aprotective gas inlet and a protective gas outlet are arranged at twoopposite ends, through which a directed protective gas flow through theprocess chamber is produced. The contaminations are removed from theprocess chamber by way of this protective gas flow.

Contaminations may still pass into the optical path of the laser beamand, by interfering with the laser beam, result in a deterioration ofthe quality of the object to be produced. In particular, the mechanicalproperties of the produced object may be deteriorated.

The object of the present invention is therefore to provide a method anda device for producing a three-dimensional object that are able to avoida deterioration of the quality of the produced object due to splashes,fumes and/or vapors exiting the irradiated material and in particular toimprove the mechanical properties of the produced object.

The object is achieved by way of a method as claimed in claim 1, adevice as claimed in claim 9, and a computer program as claimed in claim14. Further developments of the invention are specified in each case inthe dependent claims.

By matching the scanning direction of the energy beam and the main flowdirection of the gas flow to one another, it is possible to preventsplashes, fumes and/or vapors exiting the irradiated material frompassing into the optical path of the laser beam and thus the quality ofthe produced object and the mechanical properties thereof fromdeteriorating. It is therefore possible to produce objects with goodquality and good mechanical properties.

Further features and practicalities of the invention can be gatheredfrom the description of exemplary embodiments with reference to theattached figures.

FIG. 1 is a schematic view, partially illustrated in section, of anexemplary embodiment of a device for producing a three-dimensionalobject layer by layer that is suitable for carrying out the presentinvention.

FIG. 2 is a schematic illustration of the procedure of laser sinteringor laser melting according to a first embodiment of the presentinvention.

FIG. 3 is a schematic plan view of a working plane of the lasersintering device for clarifying an exposure method according to thefirst embodiment.

FIG. 4 is a schematic illustration of the scanning of a closed contouraccording to the first embodiment.

FIG. 5 is a schematic plan view of a working plane of the lasersintering device for clarifying an exposure method according to a secondembodiment of the present invention.

FIG. 6a is a schematic illustration of alternative procedures of thescanning of a region to be solidified by way of a laser beam accordingto the second embodiment.

FIG. 6b is a schematic illustration of alternative procedures of thescanning of a region to be solidified by way of a laser beam accordingto the second embodiment.

FIG. 7a is a schematic illustration of the procedure of scanning aregion to be solidified by way of a laser beam according to a thirdembodiment of the present invention.

FIG. 7b is a schematic illustration of the procedure of scanning aregion to be solidified by way of a laser beam according to a thirdembodiment of the present invention.

FIG. 7c is a schematic illustration of the procedure of scanning aregion to be solidified by way of a laser beam according to a thirdembodiment of the present invention.

FIG. 7d is a schematic illustration of the procedure of scanning aregion to be solidified by way of a laser beam according to a thirdembodiment of the present invention.

FIG. 7e is a schematic illustration of the procedure of scanning aregion to be solidified by way of a laser beam according to a thirdembodiment of the present invention.

FIG. 7f is a schematic illustration of the procedure of scanning aregion to be solidified by way of a laser beam according to a thirdembodiment of the present invention.

FIG. 8 is a schematic plan view of a working plane of the lasersintering device for illustrating an exposure method according to afourth embodiment of the present invention.

An exemplary embodiment of a device suitable for carrying out the methodaccording to the invention will be described below with reference toFIG. 1. The device illustrated in FIG. 1 represents a laser sintering orlaser melting device 1. For building the object 2, the device includes aprocess chamber 3 which is closed off from the outside by way of achamber wall 4 and serves as a build space for the object.

A container 5, which is upwardly open, is mounted in the process chamber3, in which container is arranged a carrier 6 with a substantiallyplanar upper side that is oriented substantially parallel to the upperedge of the build container. The carrier 6 serves for supporting theobject 2 to be formed and is, as is indicated in FIG. 1 by way of avertical double-headed arrow V, movable in the vertical direction by wayof a height adjustment apparatus (not illustrated). The carrier 6 ishere adjusted in each case in the vertical direction such that the upperside of a layer which is about to be solidified is located in a workingplane 7. In FIG. 1, the object 2 to be formed is illustrated in anintermediate state in which a plurality of layers of pulverulent buildmaterial has already been solidified selectively and the object 2 issurrounded by build material 8 which remains unsolidified.

The laser sintering device 1 furthermore includes a storage container 10for receiving a pulverulent build material 11 which can be solidified byway of electromagnetic radiation and a recoater 12 for depositing thebuild material 11 on the working plane 7. The present invention isparticularly advantageous for metallic build material. The recoater 12is, as indicated in FIG. 1 by way of a horizontal double-headed arrow H,movable in the horizontal direction parallel to the working plane.

The laser sintering device 1 furthermore has a laser 13 which generatesa laser beam 14. The laser beam 14 is deflected via a deflection device15 and focused, using a focusing device 16, via an input window 17 inthe wall of the process chamber 3 onto a specific point in or directlybeneath the working plane 7. It is possible by way of the deflectiondevice 15 to alter the track of the laser beam 14 such that it scans thelocations of the layer applied that correspond to the cross section ofthe object 2 to be produced.

The laser sintering device 1 furthermore includes a device for producinga gas flow 20 which flows over the working plane 7. This device includesat least one supply apparatus 21 for the gas, at least one blowingnozzle 22 on one side of the working plane 7, and at least one intakenozzle 23 on an opposite side of the working plane 7.

Finally provided is a control unit 24, by way of which the components ofthe device can be controlled in a coordinated fashion to carry out thebuild process. The control unit 20 controls, among others, the verticalmovement V of the carrier 6, the horizontal movement H of the recoater12, and the deflection device 15. The control unit 20 here controls thedeflection device 15 in a manner such that the laser beam 14 scans thelocations of the applied layer that correspond to the cross section ofthe object 2 to be produced and is turned off or screened off at thelocations that are not intended to be solidified. The control unit canalso control the output of the laser beam 14 as a function of thegeometry of the object 2 to be produced. If appropriate, the focusingdevice 16, the intensity of the laser 13, and the device for producingthe gas flow 20 (for example switching on and off the gas flow, itsintensity, its direction and so on) are also controlled by way of thecontrol unit 24. The control unit 24 can include a CPU, the operation ofwhich is controlled by way of a computer program.

Operation of the laser sintering device 1 according to the invention forproducing a three-dimensional object according to a first embodimentwill be described below with reference to FIGS. 1 and 2. FIG. 2 shows anenlargement of a detail A, which is framed in FIG. 1 by a dashed line.

In order to apply a powder layer, the carrier 6 is first lowered by aheight that corresponds to the desired layer thickness. Using therecoater 12, a layer of the pulverulent build material 11 is nowapplied. The application takes place at least over the entire crosssection of the object to be produced, preferably over the entire buildfield.

Subsequently, the cross section of the object to be produced is scannedby the laser beam 14 such that the pulverulent build material 11 issolidified at these locations. The scanning can be effected in differentexposure patterns. Said exposure patterns can be selected such that anywarping of the object to be produced is minimized In the firstembodiment, the exposure pattern consists, as shown in FIG. 7a ), ofmutually parallel lines which are scanned one after another in the samedirection.

These steps are repeated until the object is completed and can beremoved from the build space.

During scanning of the region to be solidified by way of the laser beam14, a directional gas flow which is horizontal along the working plane 7is produced. The main flow direction RG of the gas flow 20 is specifiedby the fusion line between the blowing nozzle 22 and the intake nozzle23.

According to the present invention, the main flow direction RG of thegas flow G and the scanning direction or scanning directions RL of thelaser beam 14, in which the latter scans the applied powder layer, areselected not independently from one another but such that they arematched to one another.

In the example shown in FIG. 2, a detail is shown in which the scanningdirection RL of the laser beam 14 goes from left to right. The laserbeam is incident on the working plane 7 in an incident point 30.Pulverulent build material 11 in the working plane 7 is located upstreamof the incident point 30 of the laser beam 14, with respect to thescanning direction RL, which build material is entirely or partiallymelted or solidified once it is subject to the laser beam 14. Thisresults in a region with entirely or partially melted or solidifiedmaterial 31, which is located mainly downstream of the incident point 30of the laser beam with respect to the scanning direction RL. Splashes,fumes and/or vapors 32 emerge, depending on the material used, from thisregion with entirely or partially melted or solidified material 31.

The main flow direction RG of the gas flow 20 is illustrated in FIG. 2from right to left. The scanning direction RL thus runs counter to themain flow direction RG. As a result, splashes, fumes and vapors 32,which emerge from the region with entirely or partially melted material31, are likewise diverted to the left, that is to say away from thelaser beam 14. This can prevent splashes, fumes and vapors 32 emergingfrom the irradiated material from passing into the optical path of thelaser beam 14 and thus the quality of the object 2 produced and themechanical properties thereof from deteriorating. It is thereforepossible to produce objects with good quality and good mechanicalproperties.

The opposing orientations of the scanning direction RL and the main flowdirection RG, illustrated in FIG. 2, do indeed bring the best results,but the present invention is not limited thereto.

FIG. 3 shows a plan view of the working plane 7 of the laser sinteringapparatus 1 with a coordinate system. The main flow direction RG of thegas flow 20 here runs in the positive x-direction. Furthermoreillustrated are different vectors of the scanning by the laser beam 14with different scanning directions RL. These scanning vectors RL form ineach case with the positive x axis, that is to say with the vector ofthe main flow direction RG, in the mathematically positive sense anangle y, which can range from 0 to 360° (0°≤γ≤360°). The arrangementdescribed with respect to FIG. 2 thus corresponds to an angle of 180°between the scanning vector RL and the main flow vector RG (γ=180°).However, very good results can be achieved not only for this scenario,but also if the scanning vector RL and the main flow vector RG form, inthe plan view of the working plane, an angle γ which ranges from 90° to270° (90°≤γ≤270°). In this case, the scanning vector RL has nocomponents that point in the direction of the main flow vector RG.

However, even for angles γ of less than 90° or greater than 270°, inwhich the scanning vector RL has a component which points in thedirection of the main flow vector RG, good results can still be achievedas long as the component perpendicular to the scanning direction RL issufficiently large to keep splashes, fumes and vapors 32 away from thelaser beam 14. The preferred work region (scanning vectors illustratedin FIG. 3 with solid lines) is located between the two limit angles γ1and γ2 (γ1≤γ≤γ2). Scanning directions RL between 0° and γ1 or between γ2and 360° (scanning vectors illustrated in FIG. 3 by way of dashed lines)should be avoided. The limit angles depend on the type of powder used,the laser outputs, the flow rate of the gas and other operationalparameters of the device. Generally it is possible to achieve asufficient improvement of the object quality if the angle γ lies betweenthe scanning vector RL and the main flow vector RG in the plan view ofthe working plane 7 between 22.5° and 337.5° (22.5°≤γ≤337.5°).Preferably a range is selected which lies between 45° and 315°(45°≤γ≤315°), more preferably between 60° and 300° (60°≤γ≤300°), evenmore preferably between 90° and 270° (90°≤γ≤270°). FIG. 3 shows as anexample a scenario in which the limit angles γ1 and γ2 are selected asγ1=45° and γ2=315°.

According to the first embodiment, the main flow direction RG of the gasflow 20 is fixed. Using the control unit 24, the scanning direction RLof the laser beam 14 is thus matched to this fixed main flow directionRG. This matching is effected by way of selecting in an exposure patternthe scanning direction or scanning directions RL such that the anglebetween the scanning direction or the scanning directions RL and themain flow direction RG in the plan view of the working plane 7 meets theabove-stated angle relationships.

FIG. 4 schematically illustrates an example of the scanning of a closedcontour. The contour in this example is a hexagon which is formed fromsix exposure vectors. The main flow direction RG goes from left toright. Normally, such a contour is scanned in one pass without switchingoff or screening off the laser beam. In the process, at least onesection would be scanned in the main flow direction RG, i.e. at an angleof γ=0°, which brings about the disadvantages mentioned in theintroductory part.

According to the present invention, this contour can be scanned forexample by first scanning the scanning vectors RL1, RL2 and RL3,switching off or screening off the laser beam, and then scanning fromthe same starting point the scanning vectors RL4, RL5 and RL6. The angleγ between the scanning vector RL and the main flow direction RG herealways lies in a range from 90° to 270°. Alternatively, it is alsopossible to first scan the scanning vectors RL1′, RL2′, RL3′, RL4′ andRL5′ and, once the laser beam is switched off or screened off and hasreturned to the starting point, the scanning vector RL6′. The angle γbetween the scanning vector RL and the main flow direction RG herealways lies in a range from 60° to 300°.

It is thus possible to advantageously use the invention even if scanningwith the laser beam takes place not only in one direction, but ifmultiple scanning directions are used. The principle described inconnection with the first embodiment can be applied to any desiredcontour exposures. The contour exposure is interrupted and restartedalways if otherwise the condition γ<γ1 or γ>γ2 would be met. A pluralityof interruptions of the closed contour is also possible, as is theassembly of a contour from more than one polygonal line.

A second embodiment of the present invention differs from the firstembodiment in the exposure pattern used. The region to be exposed, whichcorresponds to the cross section of the object to be produced in alayer, is divided into elongate, mutually parallel stripes S, which areexposed in succession. In each stripe, exposure takes place in mutuallyparallel vectors V, which are substantially perpendicular to thelongitudinal direction of the stripe. During the exposure of the stripeS, the region solidified by the laser moves forward in a feed directionRV, that is to say in a direction in which the individual vectors V areexposed successively.

FIG. 5 is a schematic plan view of the working plane 7 of the lasersintering device 1 for clarifying the exposure pattern of the secondembodiment. As in FIG. 3, the main flow direction RG of the gas flow 20here runs in the positive x-direction of the coordinate system. Further,for different feed directions RV, in each case an individual stripe Swith the vectors V contained therein is shown by way of example. Thesefeed directions RV form in each case with the positive x axis, that isto say with the vector of the main flow direction RG, in amathematically positive sense an angle β, which can range from 0 to 360°(0°≤β≤360°). In this case, four limit angles exist which meet therelationship β1<β2<β3<β4, wherein the ranges between 0° and β1 andbetween β4 and 360° should be avoided.

The optimum working range lies between the two limit angles β2 and β3(β2≤β≤β3). In order that the angle γ between the scanning directions RLof the individual vectors V and the main flow direction always keep tothe ranges specified in the first embodiment, the angle β is selectedsuch that it lies in a range between 112.5° and 247.5°(112.5°≤β≤247.5°), preferably between 135° and 225° (135°≤β≤225°), morepreferably between 150° and 210° (150°≤β≤210°).

Within this range, the exposure of the individual stripes can be carriedout as is illustrated in FIG. 6a . Here, a curve is shown in which theincident point 30 of the laser beam 14 is guided over a section of theworking plane 7. The scanning directions RL of two neighboring vectors Vare mutually opposed. The turnaround regions 35 (illustrated in dashedlines in FIG. 6a ) are located outside the region of the stripe S to beexposed. The laser beam 14 is switched off or screened off in theseregions.

Likewise well suited are the two regions between the limit angles β1 andβ2 (β1≤β≤β2) and between the limit angles β3 and β4 (β3≤β≤β4). In orderthat the angle γ between the scanning directions RL of the individualvectors V and the main flow direction RG always keep to the rangesspecified in the first embodiment, the individual stripes are exposed inthis case as is illustrated in FIG. 6b . Here, all vectors V have thesame scanning direction RL. After the deflection on one side of thestripe S, the laser beam here remains switched off or screened off untilit reaches the opposite side of the stripe S and is once againdeflected. The scanning direction RL, which is the same for all vectorsV, is selected here such that it has a component in the negativex-direction, or in other words such that the angle γ between thescanning directions RL of the individual vectors V and the main flowdirection RG lies between 90° and 270°. This type of exposure can ofcourse also be applied in the range between β2 and β3. Since the type ofexposure shown in FIG. 6a , however, is more efficient, it is preferablyused in the range between β2 and β3.

For the two limit angles β1 and β4, the same values apply as specifiedin the first embodiment for γ1 and γ2, i.e. 22.5°, preferably 45° andmore preferably 60° for β1 and 337.5°, preferably 315° and morepreferably 300° for β4.

Using the above-described exposure patterns for the different rangesensures that both the angle γ between the scanning directions RL of theindividual vectors V and the main flow direction RG and the angles βbetween the feed directions RV and the main flow direction RG lie withinthe angular ranges specified in the first embodiment.

Instead of dividing the cross section into elongate, mutually parallelstripes S, a division into squares, diamonds or other geometric shapescan take place, which are exposed successively.

A third embodiment of the present invention differs from the first andthe second embodiments in the exposure pattern used. FIG. 7 is aschematic illustration of the track of the scanning of a region to besolidified by a laser beam according to a third embodiment of thepresent invention.

Here, first a layer is, as described in the first embodiment, appliedand exposed (FIG. 7a ). A further layer is then applied and exposed. Thescanning direction RL of the second layer is rotated by a specifiedangle with respect to that of the first layer (FIG. 7b ). Further layersfollow, wherein the scanning direction RL for each layer is rotated bythe specified angle with respect to that of the previous layer (FIGS.7c-7f ).

The main flow direction RG of the gas flow 20 is illustrated in FIG. 7as running from top to bottom. In this case, in the step shown in FIG.7e ), the main flow direction RG and the scanning direction RL havealmost the same direction. The control unit 24 can in this case matchthe scanning direction RL to the main flow direction RG by skipping thisstep shown in FIG. 7e ) and controlling the exposure after the stepshown in FIG. 7d ) such as is shown in FIG. 7f ). Alternatively, thecontrol unit 24 can match the scanning direction RL to the main flowdirection RG such that it changes the scanning direction RL for thisstep, preferably exposes counter to the intended scanning direction.

A fourth embodiment of the present invention relates to the simultaneousproduction of a plurality of objects 2 in a container 5. FIG. 8 is aschematic plan view of a working plane of the laser sintering device,wherein a plurality of objects (2 a-2 d) are already partiallysolidified. According to the invention, in each layer preferably firstthose objects are exposed that are arranged farthest in the direction ofthe main flow direction RG (i.e. those which lie closest to the intakenozzle 23), in the illustrated example that is the object 2 a. Thefurther order of exposure is effected counter to the main flow directionRG, i.e. the object 2 b and then the object 2 c follow. At the end,those objects are exposed that are arranged closest in the direction ofthe main flow direction RG (i.e.

those which lie closest to the blowing nozzle 23), in the illustratedexample that is the object 2 d. For the exposure of the individualobjects, each of the exposure patterns mentioned in the first to thirdembodiments or a combination thereof can be used.

This procedure can be applied not only to physically separatecomponents, but also to separate cross-sectional parts of the sameobject. This procedure can likewise be used if adjacent regions of across-sectional area are exposed individually in succession.

The features of the described embodiments can be combined as desired.For example, it is possible in the third embodiment to use instead ofthe exposure of individual lines, as is described in the firstembodiment, exposure of stripes, as is described in the secondembodiment. In this case, the feed direction RV changes as shown inFIGS. 7a-f from layer to layer. Instead of the omission of anunfavorable step described in the third embodiment, it is then alsopossible to carry out the change of the scanning direction of theindividual vectors described in the second embodiment with reference toFIG. 6 b.

Similarly to the described embodiments, the present invention can alsobe applied to any desired other exposure patterns, for example tochessboard-type or diamond-type exposure patterns. It is also possibleto use further exposure patterns or exposure types in the same layer orthe same object cross section, for example contour exposures per polygonlines, which are not matched, for example because they are less crucialfor the mechanical properties of the object on account of their exposureparameters (energy density, movement speed et cetera) or their position.

The matching according to the invention between the scanning directionRL of the laser beam 14 and the main flow direction RG of the gas flow20 does not need to be carried out over the entire cross section, butcan also take place only in one partial region of the cross section tobe solidified in which the quality demands are particularly high. Inother regions, for example where the construction speed is moreimportant than the mechanical properties, this matching can be omitted.

While matching between the scanning direction RL of the laser beam 14and the main flow direction RG of the gas flow 20 in the aboveembodiments is achieved by way of the control unit 24 selecting thescanning direction RL accordingly for the specified main flow directionRG, the control unit 24 can also match, for a specified scanningdirection RL, the main flow direction RG to said scanning direction RL.This can be realized for example by way of a plurality of blowingnozzles 22 and a plurality of intake nozzles 23 being arranged in theshape of a ring and by the corresponding nozzles being switched on andthe other nozzles switched off depending on the desired main flowdirection RG. Alternatively, the blowing nozzle 22 and the intake nozzle23 can also be arranged on a rotatable carrier which is rotatedcorrespondingly depending on the desired main flow direction RG. Thecontrol unit 24 can also change the scanning direction RL or the feeddirection RV and the main flow direction RG so as to match them to oneanother.

The exposure can be interrupted, for example during scanning of thecontour shown in

FIG. 4 or in the exposure procedure shown in FIG. 6b ), not only byswitching off or screening of the laser beam, but also by scanning withthis laser beam at these locations with an increased speed which is fastenough for the energy introduction by way of the laser beam to not besufficient to solidify the pulverulent build material.

While the device for producing a gas flow in the above embodiments isdescribed such that it includes a blowing nozzle and an intake nozzle,it is also possible for a plurality of blowing nozzles to be arranged onone side of the working plane and for a plurality of intake nozzles tobe arranged on the opposite side of the working plane in each case onenext to another. It is also possible for only one or a plurality ofblowing nozzles or for only one or a plurality of intake nozzles to beprovided. The device can be constructed such that the gas flow alwaysflows over the entire working plane or be constructed such that it flowsover only part of the working plane.

Even if the present invention was described with reference to a lasersintering or laser melting device, it is not limited to laser sinteringor laser melting. It can be used for any desired methods for producing athree-dimensional object by applying, layer by layer, and selectivelysolidifying a pulverulent build material through the action of energy,for example also for laser deposition fusion. It is thus possible touse, for example, instead of a laser, a light-emitting diode (LED), anLED array, an electron beam or any other energy or beam source which issuitable for solidifying the pulverulent build material. The inventionin particular relates generally to the production of an entire objectmerely by way of applying, layer by layer, and selectively solidifying apulverulent build material.

Different types of powder can be used as build material, as are typicalfor laser sintering or laser melting, in particular metal or plasticpowders, or filled or mixed powders.

The gas used for the gas flow is preferably an inert gas, for exampleargon or nitrogen. However, the invention can also be used if, insteadof an inert gas, a process gas is used which reacts with the materialsinvolved in the process, for example for reactive deposition of thepowder material.

1. A method for producing a three-dimensional object by applying, layerby layer, and selectively solidifying a pulverulent build materialthrough the action of energy, comprising the steps: applying a layer ofthe pulverulent build material (onto a carrier or onto a previouslyapplied and at least selectively solidified layer of the build material,scanning the locations of the applied layer that correspond to a crosssection of the object to be produced using an energy beam from an energysource for selectively solidifying the pulverulent build material, andconducting a gas flow in a main flow direction over the applied layerduring the scanning with the energy beam, characterized in that thescanning direction of the energy beam and the main flow direction of thegas flow are matched to one another at least in a region of the crosssection to be solidified.
 2. The method as claimed in claim 1, in whichthe scanning direction of the energy beam and the main flow direction ofthe gas flow are matched to one another such that the angle locatedbetween them lies in a range between 22.5° and 337.5°.
 3. The method asclaimed in claim 1, in which the main flow direction of the gas flow isfixed and the scanning direction of the energy beam is matched to thisfixed main flow direction.
 4. The method as claimed in claim 1, in whichthe main flow direction of the gas flow is altered in dependence on thescanning direction of the energy beam.
 5. The method as claimed in claim1, in which the region corresponding to the cross section of the objectto be produced is divided into a plurality of partial regions which areexposed successively, each partial region is exposed in mutuallyparallel vectors which are exposed successively in a feed direction, thescanning directions of two neighboring vectors in the partial region aremutually opposed, and the feed direction and the main flow direction arematched to one another such that the angle located between them lies ina range between 112.5° and 247.5°.
 6. The method as claimed in claim 1,in which the region corresponding to the cross section of the object tobe produced is divided into a plurality of partial regions which areexposed successively, each partial region is exposed in mutuallyparallel vectors, the scanning directions of all vectors in the partialregion are substantially the same, the feed direction and the main flowdirection are matched to one another such that the angle located betweenthem lies in a range between 22.5° and 337.5°, and the scanningdirection and the main flow direction are matched to one another suchthat the angle between them is greater than or equal to 90°.
 7. Themethod as claimed in claim 1, in which the exposure pattern of at leastone region in a layer is rotated by a specified angle relative to theexposure pattern of at least one region of the previous layer, and thescanning direction and the main flow direction are matched to oneanother by way of the fact that an exposure pattern which is not matchedto the main flow direction is skipped and instead the next intendedexposure pattern is carried out, or that the scanning direction ischanged.
 8. The method as claimed in claim 1, in which the exposurepattern of at least one region in a layer is rotated by a specifiedangle relative to the exposure pattern of at least one region of theprevious layer, the region corresponding to the cross section of theobject to be produced is divided into a plurality of partial regionswhich are exposed successively, each partial region is exposed inmutually parallel vectors which are exposed successively in a feeddirection, and the scanning direction and the main flow direction arematched to one another such that, if the angle between the feeddirection and the main flow direction in a layer lies between 112.5° and247.5°, the scanning directions of two neighboring vectors in a partialregion in this layer are mutually opposed.
 9. The method as claimed inclaim 1, in which the exposure pattern of at least one region in a layeris rotated by a specified angle relative to the exposure pattern of atleast one region of the previous layer, the region corresponding to thecross section of the object to be produced is divided into a pluralityof partial regions which are exposed successively, each partial regionis exposed in mutually parallel vectors which are exposed successivelyin a feed direction, and the scanning direction and the main flowdirection are matched to one another such that, if the angle between thefeed direction and the main flow direction in a layer lies between 22.5°and 337.5°, the scanning directions of all vectors in a partial regionin this layer are the same and this common scanning direction and themain flow direction are matched to one another such that the anglebetween them lies between 90° and 270°.
 10. The method as claimed inclaim 1, in which the exposure pattern of at least one region in a layeris rotated by a specified angle relative to the exposure pattern of atleast one region of the previous layer, the region corresponding to thecross section of the object to be produced is divided into a pluralityof partial regions which are exposed successively, each partial regionis exposed in mutually parallel vectors which are exposed successivelyin a feed direction, and the scanning direction and the main flowdirection are matched to one another such that, if the angle between thefeed direction and the main flow direction in a layer lies between 0°and 60° or between 300° and 360°, the exposure pattern is skipped andinstead the next intended exposure pattern is carried out or that thefeed direction is changed, preferably counter to the intended feeddirection.
 11. The method as claimed in claim 5 in which the partialregions are mutually parallel elongate stripes, and the mutuallyparallel vectors, in which the exposure of each stripe takes place, arearranged substantially perpendicular to the longitudinal direction ofthe stripe.
 12. The method as claimed in claim 1, in which a pluralityof adjacent or spaced-apart partial regions of the cross section to besolidified are exposed successively and the order of the exposure of thepartial regions runs counter to the main flow direction, such that firstthe partial regions which are arranged farthest in the direction of themain flow direction, and finally the partial regions which are arrangedclosest in the direction of the main flow direction are exposed.
 13. Adevice for producing a three-dimensional object by applying, layer bylayer, and selectively solidifying a pulverulent build material throughthe action of energy, comprising a carrier, on which the object isbuilt, a recoater for applying a layer of the build material onto thecarrier or a previously at least selectively solidified layer of thebuild material, an energy source for introducing an energy beam into theapplied layer of the build material, a scanning device for scanning thelocations of the applied layer that correspond to a cross section of theobject to be produced with the energy beam for selectively solidifyingthe pulverulent build material, a device for producing a gas flow in amain flow direction over the applied layer during the scanning with theenergy beam, and a control unit for controlling the application of alayer and the introduction of energy, wherein the control unit includesa CPU, the operation of which is controllable by a computer program,characterized in that the control unit is adapted for controlling thedevice for carrying out a method as claimed in claim
 1. 14. The deviceas claimed in claim 13, in which the device for producing a gas flowincludes at least one blowing nozzle and/or at least one intake nozzle.15. The device as claimed in claim 14, in which the device for producinga gas flow includes a plurality of blowing nozzles and/or the pluralityof intake nozzles.
 16. The device as claimed in claim 13, in which theplurality of blowing nozzles and/or the plurality of intake nozzles isarranged in the shape of a ring and can be selectively switched tochange the main flow direction of the gas flow.
 17. The device asclaimed in claim 13, in which the device for producing a gas flow isarranged rotatably to change the main flow direction of the gas flow.18. A computer program which is capable, when executed, of controlling adevice for producing a three-dimensional object by applying, layer bylayer, and selectively solidifying a pulverulent build material throughthe action of energy such that it carries out a method as claimed inclaim 1.